The vest line is actually the less obvious abdominal muscles. The muscles involved in the Mermaid Line are the external obliques.

Mermaid lines, also known as mermaid lines, are officially called "internal and external abdominal obliques". They refer to the two V-shaped lines on both sides of the male abdomen near the top of the pelvis, because they resemble the lower part of a fish. It has a slightly contracted shape, so it is called the mermaid line

The exposure of the mermaid line is similar to that of six-pack abs and vest line, both of which require lower body fat and more developed external oblique muscles.

The vest line and mermaid line require relatively developed rectus abdominis muscles and low body fat, and everyone can practice them. Lower body fat is the key to exposing the rectus abdominis muscles. Many people's rectus abdominis muscles are relatively well developed, but they are covered by a layer of fat, so they are not exposed.